1. Field of the Invention
The present invention relates generally to blind rivets which may be used to secure two layers of material together with access from one side only, and more particularly to an improved blind rivet which drills and deburrs its own aperture through the two layers of materials and attaches the materials together in a secure, water-resistant, sealed manner.
2. Description of the Related Art
Rivets have been used as fastening members for many years, beginning with the use of hot rivets which were inserted through an aperture after heating and peened. More recently, blind rivets have been used to secure two layers of materials together while requiring access from one side only. Blind rivets are inserted into an aperture from the front side thereof, and fastened from the front side by using one of at least two techniques.
The older technique is to use a threaded means to deform the side of the rivet which has been inserted into an aperture. By turning a driving member, the inner end of the rivet is pulled toward the outside, deforming the rivet to retain it in place. Such a rivet is illustrated in U.S. Pat. No. 3,403,593, and in U.S. Pat. No. 3,453,927, both to Moore. The Moore rivets are typical of this type of blind rivet.
The newer and preferred technique is that of the so-called "pop" rivet in which a shaft extends through a hollow cylindrical rivet sleeve having an enlarged head thereon. The rivet sleeve is typically made of a material such as aluminum. A mandrel is located on the end of the shaft which is on the blind end of the rivet, adjacent the blind end of the rivet sleeve. The rivet is inserted into a pre-drilled aperture, and the shaft is placed under tension from the front of the joint to draw the mandrel against the rivet sleeve and toward the head of the rivet sleeve, radially expanding the portion of the rivet sleeve in the back of the joint.
The shaft is scored near the end attached to the mandrel, and upon the exertion of sufficient tensile force, the shaft will break off at the scored location after the rivet is set. Such blind rivets of the "pop" rivet variety are widely used today in a broad number of applications. Such blind rivets have the advantage of being easy to use, and also provide a relatively great strength-to-weight characteristic.
One of the few disadvantages such blind rivets have is that an aperture must be pre-drilled through the materials prior to the time the rivet is used. As might be expected, the art is replete with a number of proposed solutions to this problem in the form of self-drilling rivets. The Moore references mentioned above are examples of such rivets, with a drill tip being mounted on the blind end of the Moore rivets.
The Moore rivets offer several particular disadvantages which make them less than completely satisfactory. First, the Moore rivets are the type which has a threaded shaft requiring a number of rotations to set the rivet, making the installation require considerably more effort than a "pop" rivet. Secondly, the Moore rivets are difficult to manufacture, since the drill tip must be welded onto the threaded shaft. In addition, the Moore rivets will often leave a burr on the outside layer of materials drilled, which burr will prevent the head of the rivet from seating properly on the outer layer. Finally, and most significantly, the Moore rivets are expensive to manufacture, and due to this high cost are economically undesirable in most applications.
U.S. Pat. No. 3,750,518, to Rayburn, discloses a self-drilling rivet which sets in the manner of "pop" rivets by exerting a tension on a shaft. The Rayburn rivet also has the disadvantage of leaving a burr on the outer layer of material as it drills through the two layers of material to be fastened. Again, the presence of this burr may prevent the Rayburn rivet from seating properly on the outer layer of material, thus causing a weak joint. In addition, the Rayburn rivet does not provide a secure seal, since the drill head may fall off or be pushed through the remainder of the rivet. Thus, the Rayburn rivet relies entirely on the hollow rivet sleeve to form the finished rivet.
U.S. Pat. No. 3,935,786, to Murray et al., discloses another self-drilling rivet having the same disadvantages of the Rayburn rivet. The Murray et al. rivet is susceptible to leaving a burr on the outer layer of materials which may prevent the head of the rivet from being properly seated. The Murray et al. rivet, like the Rayburn rivet, does not provide a good seal since the drill head of the Murray et al. rivet is susceptible to dropping off. Finally, the Murray et al. rivet relies entirely on the hollow rivet sleeve to form the finished rivet.
Another self-drilling rivet is disclosed in U.S. Pat. No. 4,629,380, to Gunkel et al. The Gunkel et al. rivet, like all the self-drilling rivets discussed above, will likely leave a burr on the outside of the outer layer of material when the aperture is drilled for the rivet. The head of the rivet will be seated over this burr, preventing the head of the rivet from properly engaging in a flat manner the outside of the outer layer of material.
In addition, the Gunkel et al. rivet, like the other rivets above, uses a shaft which is scored or notched as the mechanism to allow the shaft to break off as the rivet is expanded. The manufacture of such a scoring or notch in the shaft is sufficiently imprecise so as to allow the amount of tensile force which is placed on the rivet as it is being expanded to vary somewhat. This may result in rivets in which the shaft breaks off before the rivet is sufficiently enlarged, resulting in substandard rivets. Another problem with rivets of this type is the difficulty in adequately controlling the strength of the weakened part of the shaft, both in torsion as well as the tensile strength. There is a tendency, therefore, of the shaft of such a rivet to twist off prematurely during the drilling phase, particularly where unexpected resistance is encountered in the material being drilled.
It is accordingly the objective of the present invention that it provide a self-drilling "pop" type rivet which overcomes the disadvantages of the art as described above. It is a primary objective of the present invention that it provide a rivet which has an improved mechanism for allowing the breakoff of the shaft such that a more controlled amount of tension may be placed on the rivet to fully expand it before the shaft breaks off. This will result in more uniformly formed rivets which will have superior holding characteristics.
It is also an objective of the present invention to provide a rivet which will be fully sealed, preventing the passage of fluid therethrough. It is an additional objective of the present invention to provide a self-drilling rivet which will remove any burrs which may otherwise prevent the proper seating of the rivet. It is a further objective of the present invention to provide a rivet which is simple of manufacture, to reduce the cost to a level below that of prior self-drilling rivets.